@article{wilkerson_kilgore_gard_steer_2015, title={Passive Intermodulation Distortion in Antennas}, volume={63}, ISSN={["1558-2221"]}, DOI={10.1109/tap.2014.2379947}, abstractNote={An analytic formulation of passive intermodulation distortion (PIM) in antennas is presented for PIM introduced by electro-thermal modulation of conductivity by current-related losses. A silver rectangular patch antenna was fabricated using a sapphire substrate isolating the thermal process from other possible sources. Two-tone testing at 990 MHz using a sweep of the tone separation from 3 Hz to 100 kHz is reported. Both transmitted and reflected PIM are characterized using a high dynamic range two-tone test system incorporating an analog canceler achieving a dynamic range of 125 dB at 1-Hz tone separation for reflection measurements, and 100 dB at 10-Hz tone separation for transmission measurements with each tone set to 32.3 dBm.}, number={2}, journal={IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION}, author={Wilkerson, Jonathan R. and Kilgore, Ian M. and Gard, Kevin G. and Steer, Michael B.}, year={2015}, month={Feb}, pages={474–482} }
 @inproceedings{steer_wetherington_wilkerson_2013, title={Investigation of close-in passive intermodulation distortion on antennas}, DOI={10.1109/aps.2013.6711784}, abstractNote={Passive intermodulation distortion (PIM) generated on antennas is experimentally investigated and shown to agree with calculations based on an electro-thermal origin. Two-tone testing is used in the investigations with tone spacings ranging from 3 Hz to 100 kHz. The two-tone measurement system has a minimum spurious-free dynamic range of 125 dB at 3 Hz tone separation. Results show that at least some of the PIM generated by an antenna is due to electro-thermal effects but it is apparent that there are sources of PIM that cannot be described by electro-thermal effects alone.}, booktitle={2013 ieee antennas and propagation society international symposium (apsursi)}, author={Steer, M. B. and Wetherington, J. M. and Wilkerson, J. R.}, year={2013}, pages={2251–2252} }
 @inproceedings{steer_wilkerson_kriplani_wetherington_2012, title={Why it is so hard to find small radio frequency signals in the presence of large signals}, DOI={10.1109/inmmic.2012.6331916}, abstractNote={The essence of radar, radio and wireless sensor engineering is extracting small information-bearing signals. This is notoriously difficult and engineers compensate by transmitting high power signals, reducing range, and spacing wireless systems in frequency and time. New understandings of passive intermodulation distortion, thermal effects, time-frequency effects, and noise are presented. It is seen that the familiar frequency-domain-based abstractions have missed important underlying physics. Through greater understanding, RF engineers can develop microwave systems with far lower levels of distortion and noise.}, booktitle={2012 Workshop on Integrated Nonlinear Microwave and Millimetre-Wave Circuits (INMMIC)}, author={Steer, M. B. and Wilkerson, J. R. and Kriplani, N. M. and Wetherington, J. M.}, year={2012} }
 @article{wilkerson_gard_steer_2010, title={Automated Broadband High-Dynamic-Range Nonlinear Distortion Measurement System}, volume={58}, ISSN={["1557-9670"]}, DOI={10.1109/tmtt.2010.2045525}, abstractNote={This paper presents an intermodulation distortion measurement system based on automated feedforward cancellation that achieves 113 dB of broadband spurious-free dynamic range for discrete tone separations down to 100 Hz. For 1-Hz tone separation, the dynamic range is 106 dB, limited by carrier phase noise. A single-tone cancellation formula is developed requiring only the power of the probing signal and the power of the combined probe and cancellation signal so that the phase shift required for cancellation can be predicted. The technique is applied to a two-path feedforward cancellation system in a bridge configuration. The effects of reflected signals and of group delay on system performance is discussed. Spurious frequency content and interchannel coupling are analyzed with respect to system linearity. Feedforward cancellation and consideration of electromagnetic radiation coupling and reverse-wave isolation effects extends the dynamic range of spectrum and vector analyzers by at least 40 dB. Application of the technique to the measurement of correlated and uncorrelated nonlinear distortion of an amplified wideband code-division multiple-access signal is presented.}, number={5}, journal={IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES}, author={Wilkerson, Jonathan R. and Gard, Kevin G. and Steer, Michael B.}, year={2010}, month={May}, pages={1273–1282} }